Packet-switched handover

ABSTRACT

A packet-switched handover from a first cell to a second cell in a cellular network is discussed. Packet-switched services are provided for a mobile station in the first cell based on a set of information relating to provision of packet-switched services and a protocol for handling provision of packet-switched services for mobile stations, said protocol being a protocol between a cell and a respective control network element. In a control network element relating to the first cell a first message is received, which indicates a request for a packet-switched handover for a mobile station. In response to said first message, a second message is sent to the second cell. This second message requests creation of a set of information relating to provision of packet-switched services for the mobile station in the second cell, and the second message belongs to said protocol for handling provision of packet-switched services for mobile stations.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates in general to packet-switched services in cellularnetworks. In particular, the invention relates to a packet-switchedhandover procedure for a mobile station changing cells.

2. Description of the Related Art

A communication system can be seen as a facility that enablescommunication sessions between two or more entities such as userequipment and/or other nodes associated with the communication system.The communication may comprise, for example, communication of voice,data, multimedia and so on. Communication systems providing wirelesscommunication for user equipment are known. Cellular communicationsystems are configured to have a cell structure, and typically theysupport communication with user equipment changing locations (mobileusers). The support for communications for mobile users may includesupport for handing existing connections from one cell to another cell.At least routing of calls or communications for a mobile user in a newcell is typically supported in cellular systems. Some examples of acellular system are the Global System for Mobile Telecommunications(GSM) and General Packet Radio Service (GPRS). GPRS providespacket-switched data services and utilizes the infrastructure of a GSMsystem. Two further examples of cellular systems are EDGE and EGPRS,which are further enhancements to GSM and GPRS. EDGE refers to EnhancedData Rates for GSM Evolution, and EGPRS refers to EDGE GPRS.

For illustrating packet-switched services in cellular system, GPRS andEGPRS systems are used below as examples. It is, however, appreciated,that similar concepts may be found also in other cellular systemssupporting packet-switched services.

In the following description, reference is made to certain ThirdGeneration Partnership Project (3GPP) technical specifications. Thesetechnical specifications are known to a person skilled in the art ofcellular networks.

FIG. 1 illustrates schematically, as an example of a cellular networksupporting packet-switched services, a GSM/GPRS network 100.Alternatively, the system 100 may be an EDGE/EGPRS network. Only some ofthe network elements of a GSM/GPRS network are illustrated in FIG. 1.The radio access network 110 comprises a number of base station systems(BSS) 112 a, 112 b. Each base station system 112 comprises a basestation controller (BSC) 114 and a number of base stations (BS) 116. Amobile station (MS) 101 communicates with a base station 116 over aradio interface. The packet-switched core network 120 of the system 100comprises a number of GPRS Supporting Nodes (GSN) 122. Each mobilestation registered for packet-switched services has a serving GSN,called SGSN, which is responsible for controlling the packet-switchedconnections to and from the mobile station. The packet-switched corenetwork 120 is typically connected to further packet-switched networksvia a Gateway GSN (GGSN).

FIG. 2 shows schematically the protocol stacks of some of the networkelements illustrated in FIG. 1 and identifies some interfaces. Theinterface between an SGSN and a BSS is called Gb. In the SGSN protocolstack and in the BSS protocol stack towards the SGSN the followingprotocols are common. The lowest protocol is called Layer 1. The secondprotocol is Network Service (NS), and the third protocol is Base StationSystem GPRS Protocol (BSSGP). The fourth protocol in the SGSN protocolstack in Link Layer Control (LLC), and the counterpart for this protocolentity is found in the MS protocol stack.

The interface between a MS and a BSS is called Um. The protocols arecommon in the MS protocol stack and in the BSS protocol stack towardsthe MS are the following: the lowest protocol is called the physicallayer (PHY), the second in the Media Access Control (MAC) protocol andthe third in the Radio Link Control (RLC) protocol. In the MS protocolstack, there is further the LLC protocol and on top of that furtherprotocols or applications. In the BSS protocol stack, data is relayedbetween the RLC protocol and the BSSGP protocol.

A GPRS or EGPRS network assigns a temporary identifier for a mobilestation wishing to have access to packet-switched service. Thisidentifier is a Packet-Temporary Mobile Subscriber Identifier (P-TMSI),and it is assigned by the SGSN. P-TMSI handling is discussed in TS23.003 and TS 24.008. A further identifier, a Temporary Logical LinkIdentifier (TLLI), is used for addressing resources allocated for GPRSservices at RLC/MAC layer on the Um interface and in the BSSGP layer onthe Gb interface. The value for TLLI is built by the MS or by SGSNeither on the basis of the Packet-Temporary Mobile Subscriber Identity(P-TMSI) or directly (random TLLI). TLLI handling is discussed in TS23.003.

A packet data protocol (PDP) context refers to information sets held inMS and GPRS Supporting Nodes (GSNs) that are used to bind the MS to anPDP address that identifies an application, PDP type and a QoS profile.PDP context functions are discussed in 3GPP TS29.060.

For identifying MS PDP contexts, the TLLI identifier is used togetherwith a Network layer Service Access Point Identifier (N-SAPI). N-SAPI isan identifier used at a Subnetwork Dependent Convergence Protocol(SNDCP) layer in a mobile station and in a SGSN.

A further identifier for identifying packet-switched services is thePacket Flow Identifier (PFI). The PFI identifier is assigned by theSGSN, and the PFI identifies a packet flow for a certain MS. A mobilestation may have more than one packet flow.

Information related to quality of service characteristics of the userdata transmission in GPRS/EGPRS for a specific packet flow is kept in aBSS Packet Flow Context (BSS PFC). A BSS PFC thus relates to one packetflow identified by a PFI. The BSS PFC is given to a BSS by the SGSN. BSSpacket flow contexts related to one MS are stored in an MS specific BSScontext identified by TLLI. Within the BSS context, a BSS PFC isidentified by the packet flow identifier PFI.

A Temporary Block Flow (TBF) is allocated radio resources on one or morepacket data channels (PDCHs) that comprise a number of RLC/MAC blockscarrying one or more upper layer PDUs. A TBF is temporary and ismaintained only for the duration of the data transfer. A TBF may operatein either GPRS or EGPRS TBF mode. Radio Resources allocated for an MSare addressed by TLLI.

In the following, resources allocated for packet-data services in aGSM/EDGE Radio Access Network (GERAN) are discussed. Depending on whichinterface is used to connect the radio access network to the corenetwork, there are two types of GERAN architectures: GERAN A/Gb mode andGERAN lu mode. The following description relates in particular to GERANA/Gb mode, thus it may not be applicable to GERAN lu mode. There are twomain identifiers for packet switched service classes and mobile stationsin GERAN A/Gb mode: the Packet Flow Identifier (PFI) and the TemporaryLogical Link Identity (TLLI).

A cell refers to a basic unit of the cellular network. Each base stationmay form a cell, or base station may be provided with transceivers,whereof each forms a cell. In a GPRS/EGPRS network, a mobile station 101is communicating with one base station (cell) at a time. When the mobilestation 101 moves, it changes cell. In a GSM network, term handoverrefers to handing over (circuit-switched) connections from the old(source) cell to a new (target) cell.

There is need also for a handover for the packet-switched connections. Apacket-switched handover would minimize the service interruption timesby allowing continuous data transfer between a MS and a cellular system,when the MS is moving from one cell to another cell. A packet-switchedhandover may be an intra-SGSN handover or an inter-SGSN handover. In anintra-SGSN handover, the source and target BSS are controlled by thesame SGSN. In an inter-SGSN handover, the source BSS is controlled by afirst (source) SGSN and the target BSS is controlled by a second(target) SGSN.

There exists a proposal in the 3GPP TSG GERAN, namely “Support ofConversational Services over the PS domain; Technical Report (Release6)” version 0.8.0, for a packet-switched handover procedure in aGPRS/EGPRS network. This proposal provides the technical solutions tosupport conversational QoS class in the GERAN A/Gb mode. ConversationalQoS class is used to carry real-time traffic flows most sensitive todelay. In this proposal, a packet-switched handover for conversationalQoS class comprises two phases: a preparation phase and an executionphase.

FIG. 3 schematically illustrates, as an example of a packet-switchedinter-SGSN handover, the preparation phase of an inter-SGSN PS handoverin accordance with the above mentioned proposal. In phase 301, a sourceBSS makes a decision to perform an A/Gb PS Handover. The source BSS thensends a PS Handover Required message 302 to the source SGSN. Thismessage 302 contains various identifiers, including a target cellidentifier. Based on the target cell identifier, the source SGSNdetermines the target SGSN, and thereafter informs the target SGSN aboutthe handover with Prepare PS Handover Request message 303. Upon receiptof this message, the target SGSN assigns a P-TMSI value for the mobilestation in phase 304. Then the target SGSN send a PS Handover Requestmessage 305 to the target BSS. In phase 306 radio resources areallocated in the target BSS for the packet-switched services relating tothe mobile station. After radio resource allocation, the target BSSsends a PS Handover Request Acknowledgement 307 to the target SGSN. Thetarget SGSN sends then a Prepare PS Handover Response message 308 to thesource SGSN. In phase 309, the source SGSN starts bi-casting packet datato the target SGSN.

In the beginning of the execution phase of the proposed packet-switchedhandover, the source SGSN sends a PS Handover Command message to thesource BSS. The source BSS, in turn, sends PS Handover Command messageto the mobile station. The P-TMSI value assigned by the target SGSN isdelivered to the mobile station in this PS Handover Command message. Themobile station changes cells from the source cell to the target cell,and after certain procedures relating to the cell change The executionphase continues with a PS Handover Complete Message sent by the mobilestation to the target BSS. The target BSS sends a PS Handover Completemessage to the target SGSN. Thereafter the target SGSN and the GGSNupdate PDP context with Update PDP Context Request and Update PDPContext Response messages. After the PDP context update in the GGSN, thetarget SGSN sends a Forward PS Handover Complete message to the sourceSGSN. The source SGSN responds with a Forward PS Handover CompleteAcknowledgement message. Thereafter BSS packet flow procedures arecarried out between the source SGSN and the source BSS. In the end ofthe execution phase, a routing area update (RAU) procedure is carriedout. The mobile station initiates this routing area update by sending aRAU Request message.

In the above discussed inter-SGSN packet-switched handover (FIG. 3), atarget SGSN needs to assign a P-TMSI for the MS for the target cellbefore the MS is residing in the target cell. In addition to the abovementioned example, a SGSN may need to assign a new P-TMSI for a MS alsoin an intra-SGSN handover. This is the case, for example, when thesource cell and the target cell belong to different routing areas (RA).

As mentioned above, the proposed packet-switched handover procedure is aquite a complex procedure having a preparation phase and an executionphase. A set of messages relating to packet-switched handover isdefined, this set comprising at least nine new messages: PS HandoverRequired, Prepare PS handover Request, PS Handover Request, PS HandoverRequest Acknowledge, Prepare PS Handover Response, PS Handover Command,PS Handover Complete, Forward PS Handover Complete, and Forwards PSHandover Complete Acknowledge. It should be also noted that failurescenarios may become quite cumbersome with such a handover procedurehaving a preparation phase and an execution phase and a significantnumber of signaling messages between various network elements.

Furthermore, there may be need for some changes also in the Routing AreaUpdate procedures, as the BSS PFC (Packet Flow Context), MM, and PDPcontexts need to be exchanged during the packet-switched handoverprocedure.

Furthermore, the mobile station should also be able to cope withpossible failures in the handover procedure. An example of such apossible failure is that access in the target cell fails and the MSreturns to the source cell.

One aim of the embodiments of the present invention is to present astraightforward procedure for a packet-switched handover.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, there is provided amethod for performing a packet-switched handover from a first cell to asecond cell in a cellular network, said method comprising the steps of:

-   -   providing packet-switched services for a mobile station in the        first cell based on a set of information relating to provision        of packet-switched services and a protocol for handling        provision of packet-switched services for mobile stations, said        protocol being a protocol between a cell and a respective        control network element,    -   receiving from the first cell in a control network element        relating to the first cell a first message indicating a request        for a packet-switched handover for a mobile station, and    -   sending, in response to said first message, to the second cell a        second message requesting creation of a set of information        relating to provision of packet-switched services for the mobile        station in the second cell, the second message being a message        of said protocol for handling provision of packet-switched        services for mobile stations.

In accordance with a second aspect of the invention, there is provided anetwork element for a cell in a cellular network providingpacket-switched services for mobile stations, said network element beingconfigured

-   -   to handle provision of packet-switched services for a mobile        station in said cell based on a set of information relating to        provision of packet-switched services and a protocol for        handling provision of packet-switched services, and    -   to initiate preparations for a packet-switched handover of the        mobile station to said cell upon receipt of a message requesting        creation of a set of information relating to provision of        packet-switched services for the mobile station, said message        being a message of the protocol for handling provision of        packet-switched services.

In accordance with a third aspect of the invention, there is provided acontrol network element for a cell in a cellular network providingpacket-switched services for mobile stations, said control networkelement being configured

-   -   to handle provision of packet-switched services for mobile        stations in at least said cell using a protocol for handling        provision of packet-switched services, and    -   to send, in response to receipt of a message indicating a        request for a packet-switched handover of a mobile station to        the cell from a further cell, to the cell a message requesting        creation of a set of information relating to provision of        packet-switched services for the mobile station in the cell.

In accordance with a fourth aspect of the invention, there is provided acellular network having a first cell, a second cell and a controlnetwork element for at least the first cell, said cellular network beingconfigured

-   -   to provide packet-switched services for a mobile station based        on a set of information relating to provision of packet-switched        services and a protocol for handling provision of        packet-switched services for mobile stations, said protocol        being a protocol between a cell and a respective control network        element,    -   to receive from the first cell in the control network element a        first message indicating a request for a packet-switched        handover for a mobile station in the first cell, and    -   to send, in response to said first message, to the second cell a        second message requesting creation of a set of information        relating to provision of packet-switched services for the mobile        station in the second cell, the second message being a message        of said protocol for handling provision of packet-switched        services for mobile stations.

In the embodiments of the invention, cells of a cellular network aretypically organized into groups. There is a control network element foreach group of cells. In a handover procedure, a first message requestinga packet-switched handover is sent from a first cell (source cell) to acontrol network element of the first cell. The control network elementof the first cell determines whether the second cell (target cell)belongs to the same group of cells as the first cell or whether afurther control network element needs to be involved in the handoverprocedure.

In the embodiments of the invention, when the control network element ofthe first cell controls also the second cell, the control networkelement of the first cell sends to the second cell the second messagerequesting creation of a set of information relating to provision ofpacket-switched services for the mobile station in the second cell.

Alternatively, if the control network element finds out that a furthercontrol network element controls the second cell, the control networkelement sends a message requesting a handover to the further controlnetwork element. This further control network element then sends to thesecond cell the second message requesting creation of a set ofinformation relating to provision of packet-switched services for themobile station in the second cell.

In the appended claims, sending of the second message in response to thefirst message covers both a packet-switched handover procedure, whereone control network element is involved, and a packet-switched handoverprocedure, where also a further control network element is involved.Furthermore, it is possible that other network elements than the furthercontrol element of the second cell are involved in the procedurefollowing the receipt of the first message. Because in normal operation,the second message is always sent in the packet-switched handoverprocedure when the first message is received, the second message is sentin response to the first message.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying drawings, in which:

FIG. 1 shows schematically a cellular communication system with whichembodiments of the invention can be used;

FIG. 2 shows schematically protocol stacks of some network elementsshown in FIG. 1;

FIG. 3 shows a message sequence chart relating to a proposedpacket-switched handover procedure;

FIG. 4 shows some messages relating to a packet-switched handover inaccordance with an embodiment of the invention;

FIG. 5 shows a message sequence chart of an intra-SGSN packet-switchedhandover in accordance with an embodiment of the invention;

FIGS. 6 a to 6 f show Tables 1 to 6 relating to messages in accordancewith an embodiment of the invention;

FIG. 7 shows some messages relating to an inter-SGSN packet-switchedhandover procedure in accordance with an embodiment of the invention;

FIG. 8 shows a message sequence chart relating to an inter-SGSNpacket-switched handover procedure in accordance with an embodiment ofthe invention;

FIGS. 9 a to 9 e show Tables 7 to 11 relating to messages in accordancewith an embodiment of the invention;

FIGS. 10 a to 10 c show Tables 12 to 14 relating to further messages inaccordance with an embodiment of the invention;

FIG. 11 shows schematically an inter-SGSN packet-switched handoverprocedure in accordance with an embodiment of the invention; and

FIG. 12 shows Table 15 relating to a Handover TLLI.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 to 3 have been discussed above in connection with thedescription of prior art.

In the following description of the embodiments of the invention,reference is often made to a GPRS or EGPRS system. It is, however,appreciated that the invention may be applicable to other cellularsystems supporting packet-switched data services.

In a cellular network there is a protocol between a cell and a controlnetwork element of the cell for handling the provision ofpacket-switched services for a mobile station. The protocol for handlingthe provision of packet-switched services typically conveys routinginformation and data transfer characteristics. Data transfercharacteristics refers here to quality of service information andsimilar characteristics. In GPRS/EGPRS a protocol between a controlelement and a cell for handling the provision of packet-switchedservices is the BSS GPRS protocol (BSSGP). The BSSGP is, in addition,responsible to provision of functionality to enable SGSN and BSS tooperate node management control functions.

For supporting packet-switched services for a mobile station, a cellneeds to know data transfer characteristics for packet flows. Typicallythere is a set of information relating to provision of packet-switchedservices for a specific mobile station. The set of information relatingto provision of packet-switched services on the Gb interface is inGPRS/EGPRS a BSS context. Furthermore, typically the set of informationcontains packet-flow-specific information for each packet flow. Thispacket-flow-specific set of information is generally called a packetflow context. In GPRS/EGPRS a packet-flow-specific set of informationrelating to the provision of packet-switched services is a BSS PacketFlow Context (BSS PFC).

A packet-switched handover refers to a mobile station changing cellsfrom a source cell to a target cell so that data transfer relating to atleast one packet flow of the mobile station is set up in the target cellwithout a significant interrupt in the packet data transfer. The lengthof the interrupt that is tolerable typically depends on thecharacteristics of the packet-switched service.

A packet-switched handover may be requested for all packet-switchedservices, that is for all packet flows, relating to the mobile stationsubject to the packet-switched handover. Alternatively, it is possiblethat a packet-switched handover is requested only for some of the packetflows relating to a mobile station. The decision for which packet flowsto request a handover is out of the scope of the present invention, andis not discussed here in detail. Similarly, the decision for whichpacket flows a requested handover is accepted and is to be performed, isnot discussed here in detail.

As the provision of packet-switched services is typically based onpacket flow contexts, packet flow contexts need to be transferred fromthe source cell to the target cell. At least packet flow contexts ofthose packet flows that are accepted for a packet-switched handover needto be transferred.

The embodiments of the invention concentrate on transfer of the set ofinformation relating to provision of packet-switched services,especially on the transfer of the packet flow contexts, from the sourcecell to the target cell. The protocol for handling provision ofpacket-switched services typically contains messages for handling(creating, modifying, deleting) a set of information relating toprovision of packet-switched services. The messages may be packet-flowspecific, that is there may be messages for creating a packet flowcontext in a cell and for deleting a packet flow context in a cell.These messages, perhaps slightly modified, can be used for transfer ofone or more packet flow context in connection with a packet-switchedhandover.

The embodiments of the invention provide a straightforwardpacket-switched handover, as the procedure concentrates on the transferof a set of information relating to provision of packet-switchedservices or, more particularly, on the transfer of packet flow contexts.A message requesting creation of a set of information relating toprovision of packet-switched services for the mobile station in a targetcell is sent in response to a message indicating a request of apacket-switched handover for the mobile station in the source cell.

It is appreciated that the message indicating a request of apacket-switched handover need not be a message of the same protocol towhich the message requesting creation of a set of information relatingto the provision of packet-switched services. It is, however, noted thatif the messages belong a single protocol, the processing of the messagesis simpler and more straightforward than if more than one protocol isinvolved.

It is appreciated that, for some reason, a mobile station subject to apacket-switched handover may already have a set of information relatingto provision of packet-switched services in the target cell. This mobilestation may, for example, have been in the target cell recently. In thiscase, there is no need to send the message for creating a set ofinformation relating to provision of packet-switched services. A messagefor modifying the set of information may be used if the data transfercharacteristics have changed.

There is thus no need define a new protocol for the packet-switchedhandover. It is sufficient to modify some existing messages of theprotocol for handling provision of packet-switched services and todefine a few new messages for the protocol. Some messages need to bedefined between two control elements, for supporting a packet-switchedhandover between a source cell and a target cell controlled by twocontrol network elements.

In the following, some embodiments of the invention are discussed inconnection with a GPRS or EGPRS system and BSS GPRS protocol. It is,however, appreciated that similar messages may be defined in otherprotocols in other cellular systems supporting packet-switched services.It is furthermore appreciated that in the following a BSS PFC is aspecific example of a packet flow context relating to a certain cell andto a certain mobile station.

In order to support conversational packet switched services in GERANA/Gb mode (GPRS, EGPRS) there is a need for a packet-switched handovermechanism. As part of the packet-switched handover mechanism it isrequired to support BSS PFC handover procedures between source andtarget network nodes.

In GERAN A/Gb mode, QoS characteristics for the data transmission aregiven in the BSS packet flow contexts (PFC). BSS PFCs related to one MSare stored into a single BSS context. In order to enable continuous datatransmission and to minimize service interruption in connection with apacket-switched handover, there is a need to handover the BSS PFC forthis MS from the source cell nodes to the target cell nodes.

In embodiments of the invention, enhanced BSS PFC procedures are definedto support handover of BSS PFCs between source and target cell nodes.Depending on whether the mobile station is moving within the cellsbelonging to BSCs controlled by the same SGSN or by different SGSNs, twohandover procedures are defined. For an inter-SGSN handover, a BSS PFCHandover procedure is used for the handover of BSS PFCs from the sourceBSS to the target BSS. For an intra-SGSN handover, a SGSN BSS PFCHandover procedure is used for the handover of SGSN BSS PFCs from thesource SGSN to the target SGSN. This is only needed in case ofInter-SGSN TBF handover.

In connection with FIGS. 4 and 5, the BSS PFC Handover procedure isdiscussed. FIG. 4 shows new messages relating to packet-switchedhandover in the source cell (left-hand side) and in the target cell(right-hand side). These signaling messages are preferably part of theBSSGP protocol.

A Handover BSS PFC Request message 401 from the source BSS to the sourceSGSN indicates a request for handover of one or more PFCs relating to amobile station. A Handover BSS PFC Accept message 402 from the sourceSGSN to the source BSS indicates an acceptance for packet-switchedhandover of one or more BSS PFCs, these BSS PFCs belonging to those BSSPFCs for which handover was requested with message 402. The handover ofBSS PFC(s) not listed in the Handover BSS PFC Accept message 402 butrequested in the message 401 may be considered rejected. This way thereis no need to specify separately BSS PFC(s) for which a handover wasrequested but not accepted. A Handover BSS PFC Reject message 403 fromthe source SGSN to the source BSS indicates rejection of handover of allthose BSS PFCs, for which handover was requested with message 402.

A Handover BSS PFC Detect message 404 from the target BSS to the targetSGSN indicates that the mobile station has successfully accessed thetarget cell. This message 404 is optional. A Handover BSS PFC Completemessage 405 from the target SGSN to the target BSS indicates thesuccessful completion of the handover procedure. A Handover BSS BFCFailure message 406 from the source BSS to the source SGSN is sent inthe case of failure of the handover procedure in the target cell. TheHandover BSS PFC Reject message 403 indicating an appropriate cause maybe sent from the source SGSN to the source BSS after the message 406, ifthe packet-switched handover fails.

These BSS PFC Handover Messages of FIG. 4 typically need to carryinformation related to the MS identification: TLLI derived from a validP-TMSI, List of PFIs identifying BSS PFC subject to handover, QoSProfiles for each corresponding BSS PFC, source cell identifier, targetcell identifier, and a TBF_Handover_Container. TheTBF_Handover_Container carries information relevant for thepacket-switched handover for each corresponding PFC. This informationincludes, for example, TBF parameters in the source cell like TBF mode,RLC mode, or radio resource assignment information in the target cell.Tables 1 to 6 provide further details.

FIG. 5 illustrates the relation between existing BSSGP signalingmessages and the BSS PFC Handover message in an intra-SGSN TBF Handover.The packet-switched handover on the Gb interface starts with a HandoverBSS PFC Request message 401 from the source BSS to the SGSN. Thismessage 401 is an example of a message indicating a request for ahandover for packet switched services of a mobile station (a firstmessage in the appended claims). The SGSN, in response to the HandoverBSS PFC Request message 401, sends to the target BSS a Create BSS PFCRequest message 501. This message 501 is an example of a messagerequesting creation of a set of information relating to packet switchedservices of the mobile station (a second message in the appendedclaims). In the BSSGP there exists a Create BSS PFC Request messagerequesting creation of one or more BSS PFC, for example, when a newpacket-switched connection is established for a mobile station. Themessage 501 initiates preparations for the packet-switched handover inthe target cell.

The existing Create BSS PFC request needs to be modified so that itincludes information elements for use in the BSSGP for use in thepacket-switched handover. The modification is to add informationelements related to the Source Cell Identifier, Target Cell Identifierand TBF Handover Source Cell Container. Otherwise there is no need tomodify create BSS PFC procedure. The target BSS responds by sending aCreate BSS PFC Accept message 502 to the SGSN. This message 502 is anexample of a message sent from the target cell and indicating acceptanceof the request for handover for packet-switched services (a thirdmessage in the appended claims). This message 502 is a modified CreateBSS PFC Accept message of the BSSGP protocol. The modification is to addto the message information elements related to Source Cell Identifier,Target Cell Identifier, TBF Handover Target Cell Container for the listof accepted PFIs and optionally TBF handover reference and Routing andLocation Area Information.

The SGSN sends to the source BSS a Handover BSS PFC Accept message 402once the SGSN has received the Create BSS PFC Accept message 502. Thismessage 402 is an example of a message sent to the first cell, themessage indicating acceptance of the handover for packet switchedservices of the mobile station (a fourth message in the appendedclaims). After the MS has moved to the target cell and thepacket-switched handover procedure has been successfully completed, thetarget BSS sends to the SGSN a Handover BSS PFC Complete message 405.This message 405 is an example of a message received from the targetcell and indicating completion of the handover for packet switchedservices of the mobile station (a fifth message in the appended claims).Before sending this Handover BSS PFC Complete message 405, the targetBSS may send to the SGSN a Handover BSS PFC Detect message 404.

Upon receiving the Handover BSS PFC Complete message 405, the SGSN sendsto the source BSS a Delete BSS PFC Request message 503. Upon receipt ofthis message 503, the source BSS deletes all the BSS packet flowcontext(s) of the mobile station. Alternatively, it is possible todelete the packet flow context(s) of the PFI(s) indicated in the message402 in the source cell upon receipt of the message 402. This may,however, cause problems in some failure scenarios. The source BSSresponds to the source SGSN by sending a Delete BSS PFC Accept message504. In the BSSGP protocol, there exist a message for deleting BSS PCFsand for accepting deletion of the BSS PFCs. Messages 503 and 504 may bethese existing BSSGP protocol messages. The message 503 is an example ofa message for deleting a set of information relating to packet switchedservices of the mobile station (a sixth message in the appended claims).

FIGS. 6 a to 6 f show Tables 1 to 6, which give, by the way of example,details about the content of the Handover BSS PFC messages 401 to 406.Tables 1 to 6 show information elements of the protocol data units(PDUs), and the types of the information elements. Furthermore, Tables 1to 6 show the mandatory (M) or optional (O) presence of the informationelements in the PDUs, the format of the information elements and thelength of the information elements. The format is V or TLV (Type,Length, Value). Blank entries in Tables indicate that the presence,content or format of the information is to be specified.

Table 1 shows the content of a Handover-BSS-PFC PDU, which relates tothe Handover BSS PFC Request message 401. Table 2 shows the content of aHandover-BSS-PFC-ACK PDU, which relates to the Handover BSS PFC Acceptmessage 402. Table 3 shows the content of a Handover-BSS-PFC-NACK PDU,which relates to the Handover PCF Reject message 403. Table 4 shows theHandover-BSS-PFC-Detect PDU, which relates to the Handover BSS PFCDetect message 404. Table 5 shows the Handover-BSS-PFC-Complete PDU,which relates to the Handover BSS PFC Complete message 405. Table 6shows a Handover-BSS-PCF-Failure PDU, which relates to the Handover BSSPFC Failure message 406.

For each of the PDUs shown in Tables 1 to 6, there is need to define anew PDU type.

For an inter-SGSN packet-switched handover, a SGSN BSS PFC Handoverprocedure is defined in embodiments of the invention. FIG. 7 showsmessages relating to the SGSN BSS Handover only. These signalingmessages are preferably part of the BSSGP protocol.

FIG. 8 shows messages relating to an inter-SGSN packet-switchedhandover, that is also messages between the SGSNs and the BSSs. The SGSNBSS PFC procedure is initiated by the source SGSN upon receipt of aHandover BSS PFC Request message 401 (see FIG. 8), if thepacket-switched handover is an inter-SGSN handover. The Handover SGSNBSS PFC Request message 701 indicates a request for handover of one ormore PFC.

Upon receiving the Handover SGSN BSS PFC Request message 701, the targetSGSN may perform SGSN Context handover, Update PDP Context and LocationUpdate procedures in the same manner and order as during Routing AreaUpdate procedures. Alternatively, the Handover SGSN BSS PFC Requestmessage 701 may carry information for transferring PDP and MM contextsto the target SGSN. In this case, it is sufficient to carry out theUpdate PDP Context and Location Update procedures between the sourceSGSN and the target SGSN.

FIG. 7 shows these two scenarios for a SGSN BSS PFC Handover procedure.In the procedure shown in the left-hand side of FIG. 7, the HandoverSGSN BSS PFC Request message 701 carries information for transferringPDP and MM contexts to the target SGSN. In the alternative procedureshown in the right-hand side of FIG. 7, a SGSN context transferprocedure is used for transferring PDP and MM contexts.

In the procedure in the left-hand side of FIG. 7, the source SGSN sendsa Handover SGSN BSS PFC Request message 701 to the target SGSN. Thismessage 701 indicates the request for handover of one or more PFCs of amobile station and contains information for transferring PDP and MMcontexts to the target SGSN. The target SGSN indicates acceptance of thehandover request of one or more PFCs by sending a Handover SGSN BSS PFCAccept message 702. Thereafter the Update PDP Context procedure andUpdate Location procedure are carried out between the source SGSN andthe target SGSN.

In the alternative procedure in the right-hand side of FIG. 7, thesource SGSN sends a Handover SGSN BSS PFC Request message 701 to thetarget SGSN. Thereafter a SGSN Context Transfer Procedure is carried outbetween the source SGSN and the target SGSN. A SGSN Context Acknowledgemessage from the target SGSN to the source SGSN indicates acceptance ofthe request for handover in this alternative procedure. The SGSN Contexttransfer procedure signaling messages need to be enhanced with newinformation elements related to TBF handover. The accepted BSS PFC arespecified in the SGSN Acknowledge message. The Update PDP Contextprocedure and the Update Location procedure are carried out between thesource SGSN and the target SGSN similarly as in the procedure shown inthe left-hand side of FIG. 7.

Upon receiving the Handover SGSN BSS PFC Request message 701, the targetSGSN sends to the target BSS the Create BSS PFC Request 501. The targetBSS acknowledges the handover of some or all PCFs with the Create BSSPFC Accept message 502, as discussed above in connection with FIG. 5.This signaling between the target SGSN and the target BSS is carried outbefore sending the Handover SGSN BSS PFC Accept message 702 or the SGSNcontext transfer.

As FIG. 8 shows, the packet-switched handover continues by the sourceSGSN sending a Handover BSS PFC Accept message 402 to the source BSS.The message 402 is sent by the source SGSN after receipt of the HandoverSGSN BSS PFC Accept message 702 or receipt of the SGSN ContextAcknowledge message. Similarly as in an intra-SGSN packet-switchedhandover, the target BSS sends a Handover BSS PFC Complete message 405if the mobile station successfully accesses the target cell. In theinter-SGSN handover, this message is sent to the target SGSN.

As shown in FIGS. 7 and 8, the target SGSN indicates a successfulcompletion of the SGSN BSS PFC Handover procedure for the acceptedPFC(s) by sending a Handover SGSN BSS PFC Complete message 703 to thesource SGSN. After receiving this message 703, the source SGSN deletesBSS PFC in the source cell by means of a Delete BSS PFC Request message503, similarly as in an intra-SGSN handover.

The Handover SGSN BSS PFC Request message 701 carries parameters relatedto the MS and TBF handover. Some examples of these parameters are thefollowing: IMSI, Tunnel Endpoint Identifier Signaling, PFI list, sourcecell identifier, target cell identifier, TBF handover Container andImplicitRAUContainer. The TBF Handover Container carries informationrelevant for TBF handover for each corresponding PFC, for example TBFparameters in the source cell like TBF mode and RLC mode.

It is appreciated that the Handover SGSN BSS PFC Request message 701 mayalso be used as an implicit RAU request, such that Information Elementsas in RAU Request are included in the Handover SGSN BSS PFC Requestmessage 701 in RAU Container.

In addition to the message 701, 702 and 703 further messages for theSGSN BSS PFC handover may be defined. A Handover SGSN BSS PFC Rejectmessage may be sent from the target SGSN to the source SGSN. Thismessage indicates the failure of packet-switched handover procedureand/or rejection of handover for all PFCs for which handover wasrequested. This Handover SGSN BSS PFC Reject message may also be sentafter the Handover SGSN BSS PFC Accept or SGSN Context Acknowledgemessage.

A Handover SGSN BSS PFC Failure message, from the source SGSN to thetarget SGSN, indicates the failure of packet-switched handover procedurein the target cell. A mobile station may fail to access the target celland may return to the source cell. The source BSS/SGSN notices that themobile station is returning to the source cell, and the source SGSNinforms the target SGSN of a failure in the handover procedure. Thismessage may also be sent after the Handover SGSN BSS PFC Accept message702 or SGSN Context Acknowledge message.

It is appreciated that if a Gb-flex solution is used, there is no needfor the SGSN BSS PFC Handover procedure. In a Gb flex solution a mobilestation may move in a pool area consisting of a plurality of cellswithout changing GSNs. One or more GSNs in parallel serve the pool area,and all cells controlled by a Base Station Controller belong to the oneor more pool areas.

FIGS. 9 a to 9 e shows Tables 7 to 11, which list, by the way ofexample, information elements in the Handover SGSN BSS PFC messages.Furthermore, Tables 7 to 11 show the mandatory (M) or optional (O)presence of the information elements in the protocol messages, andTables 7 to 11 refer to Sections of TS specifications for furtherinformation.

Table 7 lists information elements relating to the Handover SGSN BSS PFCRequest message 701. The PDP Context in Table 7 refer to the PDPContext(s) of the PFI(s) for which handover is requested. It is notedthat the SAPIs and NSAPIs listed in Table 7 are part of the PDPContexts. Table 8 lists information element relating to the HandoverSGSN BSS PFC Accept message 702. Table 9 lists information elementsrelating a Handover SGSN BSS PFC Reject message. Information element“Cause” may be used for indicating the cause for a rejected handoverrequest, for example, unavailability of resources in the target cell.Table 10 lists information elements in the Handover SGSN BSS PFCComplete message 703. Table 11 lists information elements in theHandover SGSN BSS PFC Failure message.

A packet switched handover performed in the above discussed manner doesnot introduce any changes in the existing BSS PFC procedures forcreating and deleting the BSS PFCs. Some new Information Elements may berequired in the CREATE BSS PFC signaling messages. These elements arelisted, by way of example, in Tables 12 to 14 shown in FIGS. 10 a to 10c.

Table 12 lists Information Elements of a Create-BSS-PFC PDU. This PDUallows a SGSN to request that a BSS creates or modifies a BSS PacketFlow Context. The following information elements listed in Table 12 arenew in the Create-BSS-PFC PDU: source cell identifier (SourceCell ID),target cell identifier (TargetCell ID), and TBF parameters in the sourcecell (TBC Handover Source Cell Container).

It is appreciated that a single Create BSS PFC message is preferablyused for creating a plurality of PFCs to be subject to a handoverprocedure at a time. All PCFs of a mobile station to be subject to ahandover procedure are thus preferably listed in one Create BSS PFCmessage.

Table 13 lists Information Elements of a Create-BSS-PFC-ACK PDU. ThisPDU allows the BSS to acknowledge a request from the SGSN for thecreation or modification of a BSS Packet Flow Context. The followinginformation elements are new: TBF Handover Target Cell Container, TBFHandover reference, and Routing and Location related IE. The TBFHandover Target Cell Container contains the information indicated in theType/Reference column. Similarly, the Routing and Location relatedinformation element contains the information indicated in theType/Reference column. There should preferably be in theCreate-BSS-PFC-ACK PDU one PFI information element and one ABQPinformation element for each PFI whose creation is acknowledged inconnection with the packet-switched handover.

Table 14 lists Information Elements of a Create-BSS-PFC-NACK PDU. ThisPDU allows the BSS to respond negatively to a request for creating a BSSPacket Flow Context. There should be one PFI information element foreach PFI whose creation is negatively acknowledged in connection withthe packet-switched handover.

The above discussed enhanced BSS PFC procedures (that is BSS PFCHandover and SGSN BSS PFC Handover) need not introduce any changes tothe existing air interface procedures. New information elements are,however, needed in some RLC/MAC control messages, for example in aPacket Cell Change Order message. The Packet Cell Change Order messageneeds to be enhanced with a <TBF_handover_struct> containing thefollowing information on the target cell: list of PFIs for whichresources are allocated in the target cell, and a TBF Target CellContainer. The TBF Target Cell Container contains the followinginformation: UL TBF parameters including MAC parameters (PDCH mapping,TFI, USF) and RLC parameters (channel coding, RLC reset); DL TBSparameters including MAC parameters (PDCH mapping, TFI) and RLCparameters (RLC reset); target cell frequency parameters; PSI instancesincluding a set of instances from the PSI such as GPRS cell options,access bursts type and other information that enables the access in theGPRS target cell; and TBF Handover reference.

It is furthermore possible that signaling messages relating to thepacket-switched handover procedure contain information about RLCbuffers, so that RLC buffers may be relocated in connection with thepacket-switched handover procedure.

It is appreciated that in some embodiments of the invention, it ispossible to use TLLI values of a local type or of a foreign type. Alocal type for the TLLI identifier is defined for use in a cell forwhich a P-TMSI has been assigned by the SGSN. A foreign type of TLLIidentifier is defined for use in a cell for which no P-TMSI value hasbeen assigned.

It is appreciated that some of Tables 1 to 13 mention a Handover TLLI.This Handover TLLI is used in other embodiments of the invention. TheHandover TLLI is a type of TLLI, which is valid both in the source celland in the target cell. The value of the Handover TLLI is typicallydetermined based on a value of the P-TMSI identifier in the source cell.The Handover type of TLLI is valid both in the source cell and in thetarget cell for transmitting packet-switched data between the cellularnetwork and the mobile station. The Handover type may be validirrespective of there having been assigned a value of the P-TMSI for thetarget cell. This means that the Handover TLLI may be used before andafter a value for the P-TMSI identifier is assigned for the target cell.The Handover TLLI may be alternatively for use in the source cell and inthe target cell until a value of the P-TMSI assigned for the target cellis in use in the target cell. Taking a value of the P-TMSI in use in thetarget cell typically involves the network informing the mobile stationabout the value of the P-TMSI for the target cell and the mobile stationacknowledging this value.

It is thus possible to use the handover TLLI for packet data transfer inthe source cell and in the target cell, for example, in the followingcircumstances relating to the value of the P-TMSI for the target cell.Firstly, the Handover TLLI may be used before a value of P-TMSI isassigned for the target cell. Secondly, the Handover TLLI may be usedafter a value of P-TMSI has been assigned for the target cell, but themobile station is not yet aware of the P-TMSI value for the target cell.Thirdly, the Handover TLLI may be used after the mobile station hasreceived information indicated the value of the P-TMSI for the targetcell but the mobile station has not yet acknowledged this value.

The use of Handover TLLI provides the advantage that the serviceinterruptions are shorter during the packet-switched handover procedurethan in a case, where local and foreign TLLI values are used.

In some embodiments of the invention especially applicable to GPRS/EGPRSsystems, the Handover TLLI is computed independently by each of thenodes involved in a packet-switched handover from the source P-TMSI, inother words from the P-TMSI value in use by the MS upon detection of aneed for a packet-switched handover. The Handover TLLI, similarly as theother defined TLLI types, consists of 32 bits, numbered from 0 to 31 byorder of significance, with bit 0 being the LSB. The Handover TLLI maybe defined as shown in Table 15 in FIG. 12. In Table 15, the left-mostsix columns specify the bits of the TLLI identifier. The column on theright specifies the type of the TLLI identifier.

In Table 15, as discussed in TS 23.003, ‘T’, ‘R’, ‘A’ and ‘X’ indicatebits that can take any value for the type of TLLI. More precisely, ‘T’indicates bits derived from a P-TMSI, ‘R’ indicates bits chosenrandomly, ‘A’ indicates bits chosen by the SGSN, ‘G’ indicates bitsderived from the assigned G-RNTI and ‘X’ indicates bits in reservedranges. ‘H’ bits, similarly as ‘T’ bits, indicate bits derived from aP-TMSI.

As mentioned above, the Handover TLLI may be determined independently byan MS and a SGSN that have a valid P-TMSI. The Handover TLLI may bedetermined as Table 15 in FIG. 12 indicates. In other words,

-   -   bits 31 down to 30 are set to 0;    -   bit 29 is set to 1; and    -   bits 28 down to 0 are set equal to bits 28 to 0 of the P-TMSI        assigned for the source cell.

Handover TLLI may be built from the P-TMSI because, as discussed belowin detail, the source P-TMSI is known and kept by all the nodes involvedin packet-switched handover in the source cell and the target cell.

It is appreciated that the table in FIG. 12 does not represent the onlypossible way to determine a value for the Handover TLLI. However, thisdefinition is done considering the definition of the local and foreignTLLI, to differentiate handover TLLI from these values.

It is appreciated that in more general terms the P-TMSI and the TLLIare, respectively, a first identifier used for identifying a mobilestation and a second identifier used for identifying resources allocatedfor packet-switched services for the mobile station. The Handover TLLIis, in more general terms, a type for the second identifier for a mobilestation entering or having entered a second cell from a first cell, thistype of the second identifier being for use in both the first cell andthe second cell for transmitting packet-switched data between thecellular network and the mobile station.

FIG. 11 shows an inter-SGSN packet-switched handover in accordance withan embodiment of the invention in more detail. The use of the HandoverTLLI is discussed in more detail in connection with FIG. 11.

Step 1101 in FIG. 11 represents measurement reporting by the mobilestation. The source BSS typically identifies the MS as a packet-switchedhandover capable and identifies the target cell. Based on informationabout the target cell, the source BSS sends the Handover BSS PFC Requestmessage 401 to the source SGSN to request BSS PFC handover to the targetcell. The source SGSN based on the target cell identifier in the message401 determines whether the handover is an intra-SGSN or inter-SGSNhandover. In the case of Inter-SGSN handover, the SGSN initiateshandover of the BSS PFC context of this MS to the Target SGSN by sendingthe Handover SGSN BSS PFC Request message 701.

The target SGSN identifies the target BSS and if the target SGSN canaccept the request, the target SGSN sends a CREATE BSS PFC Requestmessage 501. Before sending the message 501, the target SGSN may assigna P-TMSI for the target cell (new P-TMSI) and determine a Handover TLLIbased on the P-TMSI in the source cell (old P-TMSI). The Handover TLLIis used in the message 501, as indicated in Table 12. If Handover TLLIis not used, the TLLI in the message 501 is the local TLLI based on thenew P-TMSI.

The target BSS tries to reserve the radio resources, that is, the targetBSS assigns timeslots for the TBF handover in step 1102. Aftersuccessful radio resource reservation the target BSS sends a CREATE BSSPFC Accept message 502 to the target SGSN. The Handover TLLI isadvantageously used in the message 502. Alternatively, the same localTLLI is used as in the message 501.

When the Handover TLLI is used, the target BSS may differentiate betweenthe BSS PFC subject to a handover procedure and those BSS PFCs that arenot subject to a handover procedure based on the TLLI type in themessage 501. For BSS PFCs subject to a handover procedure, the TLLI typein the message 501 is handover. For BSS PFCs not subject to a handoverprocedure, the TLLI type in the message 501 is local.

The target SGSN upon receipt of the CREATE BSS PFC Accept message 502sends to the source SGSN the Handover SGSN BSS PFC Accept message 702.The source SGSN derives the Handover TLLI from its P-TMSI, and thesource SGSN uses this Handover TLLI value for the signaling messages aswell as for data transfer until the completion of the handover. Step1103 represents that data flows are forwarded to the target SGSN fromthe source SGSN at this point.

The source SGSN sends the HANDOVER BSS PFC ACCEPT message 402 to thesource BSS. The source BSS sends a Packet Cell Change Order (PCCO)message 1104 to the MS. The PCCO message has a <TBF_Handover_Struct>that provides the MS with the necessary information related to TBFhandover on the target cell. The MS receives the PCCO message 1104. Ifthe MS is polled by the source BSS, the MS sends a PACKET CONTROLACKNOWLEDGMENT message 1105 after which the MS may switch to a new cell.The MS upon receipt of the PCCO message 1104 derives the Handover TLLIfrom its P-TMSI. The MS uses the Handover TLLI value for signalingmessages and for uplink data, until the MS receives the new P-TMSIduring RAU procedure.

When the MS is in the target cell, it sends a PACKET CONTROLACKNOWLEDGMENT message 1106 to the target BSS to request the timingadvance from the network. The target BSS responds by sending a PACKETUPLINK ASSIGNMENT message 1107 containing a valid timing advanceinformation and TBF assignment for the target cell. Thereafter the MSsends a PACKET PSI Status message 1108 to request the missing systeminformation (P)Sis ((Packet) System Information). The target BSS sendthe Requested PSIs 1109 to the MS. Thereafter the target BSS sends aHANDOVER BSS PFC COMPLETE message 405 to the target SGSN to indicatethat the TBF Handover is completed.

The target SGSN initiates the Update PDP context procedure 1110 with theGGSN as well as the Update Location procedure with the HLR. After theseprocedures, the uplink and downlink data flows are redirected in step1111 to be between the target SGSN and the GGSN.

The target SGSN sends a HANDOVER SGSN BSS PFC COMPLETE message 703 tothe source SGSN to indicate that the TBF handover to the target cell iscompleted. The target SGSN initiates the deletion of the BSS PFCs in thesource cell by sending the Delete BSS PFC Request message 503. TheHandover TLLI may be used in these messages. If the Handover TLLI is notused at all, the local TLLI is used in these messages. The source BSSremoves the BSS PFC for this MS and sends a BSS PFC delete acceptmessage 504 to the source SGSN.

The target SGSN and the mobile station carry out an Intra-SGSN RoutingArea Procedure. This involves the following messages and functions: aRouting Area Update Request message 1112, security functions 1113, aRouting Area Update Accept message 1114, and a Routing Area UpdateComplete message 1115.

In the case of TBF handover the target SGSN has already all the MMcontexts and PDP contexts for the MS. This is because the messages 701,702 and 703 are interpreted as implicit RAU messages (see FIG. 11).There is thus no need for an Inter-SGSN RAU procedure.

As a packet-switched handover procedure involves procedures to beperformed both in the source cell and in the target cell, it is possiblethat a failure occurs in the source cell or in the target cell. In thefollowing some failure scenarios are discussed briefly. It isappreciated that the messages defined above are sufficient to deal withmany failures.

A packet-switched handover may fail in the source cell mainly due to thelack of resources in the target cell, loss of signaling messages or SGSNContext Transfer Failure. In the Target cell, a packet-switched handovermay fail due to the failure of Initial Access at target cell, failure ofthe Update of PDP Contexts or Update of the Location Area Update. Inthis case the MS is allowed to go back to the source cell. The MS mayalso release the TBF and try to make an access at the target cell via(P)CCCH.

A packet-switched handover may fail while the MS is still in the sourcecell due to the lack of resources in the target cell, either on the airinterface or even in the link to the BSS. The target SGSN may determineimmediately without initiating any Create BSS PFC procedure that thetarget SGSN cannot accept the HANDOVER SGSN BSS PFC Request message. Inthis case the target SGSN will send a HANDOVER SGSN BSS PFC REJECTmessage back the source SGSN. The cause for this can be that the targetSGSN has no resources available on the link to the target BSS.

If the target BSS cannot allocate any resources for the list of PFIs,the target BSS will send a CREAT BSS PFC NACK message to the targetSGSN. Target SGSN will inform the source SGSN by means of HANDOVER SGSNBSS PFC FAILURE message. The target SGSN also deletes the MM and PDPcontext for this MS. The source SGSN informs the source BSS about theresource unavailability by means of HANDOVER BSS PFC REJECT message. Inthis case the source BSS may order the MS in another NC mode or thesource BSS may initiate handover procedure in another cell.

If resources in the target cell have been assigned but the initialaccess in the target cell fails, the MS may return to the source celland send a PACKET CELL CHANGE FAILURE message with the appropriatecause. The source BSS and the source SGSN have still the BSS PFCs, MMand PDP contexts for this MS. The source BSS may order the MS in anotherNC mode or it may initiate the packet-switched handover in another cell.The resources assigned in the target cell need to be released. Thesource BSS sends a Handover BSS PFC FAILURE message with the appropriatecause to the source SGSN. Upon receipt of this message source SGSN sendsthe HANDOVER SGSN BSS PFC FAILURE message to the target SGSN to indicatethat the packet-switched handover has failed. The target SGSN will alsodiscard any buffered data it has received for this MS, and it willinitiate a delete BSS PFC procedure in the target cell.

It is appreciated that a network element for a cell (typically a basestation) and a control network element of a cell (for example, a SGSN)may be modified to support embodiments of the invention. Typically, themodifications may be made by updating suitable software relating to theprotocol for handling provision of packet-switched services.

It is appreciated that the names of the signaling messages may differfrom the names mentioned in the above description. It is furthermoreappreciated that the contents of the messages may also differ from thecontent of the messages described above. The details of the embodimentsof the invention are intended to enhance understanding of the invention,not to restrict the invention only to certain messages.

It is appreciated that in the description and in the appended claims theterm “packet flow” refers to a sequence of data packets, which arerelated to each other. A packet flow may, for example, contain datarelating to one upper-level data connection or session. Alternatively, apacket flow may carry information relating to more than one connectionor session.

It is appreciated that in the appended claims providing packet-switchedservices for a mobile station refers to any packet data transfer betweena mobile station and a cellular network.

It is appreciated that a set of packet data contexts refers to one ormore packet data context.

Although preferred embodiments of the apparatus and method embodying thepresent invention have been illustrated in the accompanying drawings anddescribed in the foregoing detailed description, it will be understoodthat the invention is not limited to the embodiments disclosed, but iscapable of numerous rearrangements, modifications and substitutionswithout departing from the spirit of the invention as set forth anddefined by the following claims.

1. A method, said method comprising: providing packet-switched servicesfor a mobile station in a first cell based on a set of informationrelating to provision of packet-switched services and a protocol forhandling provision of packet-switched services for mobile stations, saidprotocol being a protocol between a cell and a respective controlnetwork element, receiving from the first cell in a control networkelement relating to the first cell a first message indicating a requestfor a packet-switched handover for a mobile station, and sending, inresponse to said first message, to a second cell a second messagerequesting creation of a set of information relating to provision ofpacket-switched services for the mobile station in the second cell, thesecond message being a message of said protocol for handling provisionof packet-switched services for mobile stations.
 2. A method as definedin claim 1, wherein packet-switched services are provided for the mobilestation by providing at least one packet flow and said first messageindicates a set of packet flows relating to the mobile station to behanded over.
 3. A method as defined in claim 1, wherein packet-switchedservices are provided for the mobile station by providing at least onepacket flow and said second message indicates a set of packet flowsrelating to the mobile station to be handed over.
 4. A method as definedin claim 1, wherein packet-switched services are provided for the mobilestation by providing at least one packet flow, said set of informationrelating to provision of packet-switched services comprises at least onepacket flow context, and said second message is a message requestingcreation of at least one packet flow context in the second cell.
 5. Amethod as defined in claim 4, wherein said first message indicates atleast one packet flow context relating to the mobile station.
 6. Amethod as defined in claim 4, wherein said second message indicates atleast one packet flow context relating to the mobile station.
 7. Amethod as defined in claim 1, wherein said first message is a message ofsaid protocol for handling provision of packet-switched services formobile stations.
 8. A method as defined in claim 1, wherein said secondmessage contains information identifying the first cell and the secondcell.
 9. A method as defined in claim 1, wherein resources forpacket-switched services in a cell are defined as temporary block flowsand said second message contains temporary block flow parameters of themobile station in the first cell.
 10. A method as defined in claim 1,wherein the second message contains an identifier for identifyingresources allocated in a cell for packet-switched services for themobile station, the identifier having a value valid in the first celland in the second cell.
 11. A method as defined in claim 1, furthercomprising receiving from the second cell a third message indicatingcreation of said set of information relating to provision of packetswitched services in the second cell.
 12. A method as defined in claim11, wherein said third message indicates a set of packet flows, said setof packet flows being accepted for the packet-switched handover.
 13. Amethod as defined in claim 1, further comprising sending to the firstcell a fourth message, said fourth message indicating acceptance of thepacket-switched handover for the mobile station.
 14. A method as definedin claim 13, wherein said fourth message indicates a set of packetflows, said set of packet flows being accepted for the packet-switchedhandover.
 15. A method as defined in claim 1, further comprisingreceiving from the second cell a fifth message, said fifth messageindicating completion of the packet-switched handover for the mobilestation.
 16. A method as defined in claim 15, wherein said fifth messageindicates a set of packet flows, said set of packet flows being acceptedfor the packet-switched handover.
 17. A method as defined in claim 1,further comprising sending to the first cell a sixth message fordeleting a set of information relating to provision of packet switchedservices of the mobile station, said sixth message being a message ofsaid protocol for handling packet switched services for mobile stations.18. A method as defined in claim 1, further comprising: controllingpacket-switched services in the first cell by said control networkelement, controlling packet-switched services in the second cell by afurther control network element, and sending a seventh message from thecontrol network element to the further control network element, saidseventh message indicating a request for a packet-switched handover fromthe first cell to the second cell, wherein said further control networkelement is sending the second message upon receiving the seventhmessage.
 19. A method as defined in claim 18, wherein the seventhmessage contains sets of information relating to packet data protocolsand mobility management.
 20. A method as defined in claim 18, furthercomprising carrying out a procedure relating to transfer of sets ofinformation relating to packet data protocols and mobility managementbetween said control network element and said further control networkelement.
 21. A method as defined in claim 18, further comprising sendingan eighth message from said further control network element to saidcontrol network element, said eighth message indicating acceptance ofthe packet-switched handover.
 22. A method as defined in claim 21,further comprising sending a ninth message from said further controlnetwork element to said control network element upon receipt of amessage indicating completion of the handover in the second cell, saidninth message indicating completion of the packet-switched handover. 23.A method as defined in claim 1, wherein said protocol for handlingprovision of packet-switched services for mobile stations is a BaseStation Systems (BSS) General Packet Radio Service (GPRS) protocol. 24.A method as defined in claim 1, wherein packet-switched services areprovided for the mobile station by providing at least one packet flow,said set of information relating to provision of packet-switchedservices comprises at least one base station system packet flow context,and said packet-switched handover is a base station system packet flowcontext handover.
 25. An apparatus being configured to handle provisionof packet-switched services for a mobile station in a cell based on aset of information relating to provision of packet-switched services anda protocol for handling provision of packet-switched services, and toinitiate preparations for a packet-switched handover of the mobilestation to said cell upon receipt of a message requesting creation of aset of information relating to provision of packet-switched services forthe mobile station, said message being a message of the protocol forhandling provision of packet-switched services.
 26. An apparatus asdefined in claim 25, said apparatus being a base station supporting aGeneral Packet Radio Service or an EDGE General Packet Radio Service.27. A network element, said network element being configured to handleprovision of packet-switched services for mobile stations in at least acell using a protocol for handling provision of packet-switchedservices, and to send, in response to receipt of a message indicating arequest for a packet-switched handover of a mobile station to the cellfrom a further cell, to the cell a message requesting creation of a setof information relating to provision of packet-switched services for themobile station in the cell.
 28. A network element as defined in claim27, said network element being a General Packet Radio Service (GPRS)Supporting Node for a cellular network supporting a General Packet RadioService or an EDGE General Packet Radio Service.
 29. An apparatus beingconfigured to provide packet-switched services for a mobile stationbased on a set of information relating to provision of packet-switchedservices and a protocol for handling provision of packet-switchedservices for mobile stations, said protocol being a protocol between acell and a respective control network element, to receive from a firstcell in a control network element a first message indicating a requestfor a packet-switched handover for a mobile station in the first cell,and to send, in response to said first message, to a second cell asecond message requesting creation of a set of information relating toprovision of packet-switched services for the mobile station in thesecond cell, the second message being a message of said protocol forhandling provision of packet-switched services for mobile stations. 30.An apparatus as defined in claim 29, said apparatus being a cellularnetwork supporting a General Packet Radio Service or an EDGE GeneralPacket Radio Service.